this information coming from an affidavit of a top f.b.i. official, giving a lot of details about the evidence that authorities believe they have. they say they have video that reveals the two suspects that they say are involved in the boston marathon bombing showed up to the scene, walking out of this video footage about 11 minutes before both of those bombs went off. both of the men were carrying large knapsacks according to the paperwork and they detached from the crowd, repositioned and bomber two, dzhokhar tsarnaev, the man in custody now, the man here in the hospital, is seen slipping his knapsack on to the ground precisely what this agent writes, approximately 30 seconds before the first explosion he lifts his phone to his ear as if he's speaking on his cell phone and keeps it there for approximately 18 seconds. a few seconds after he finishes the call, the large crowd of people around him can be seen reacting to the first explosion. virtually every head turns to the east, towards the finish line and stares in that direction in appare